The present invention relates to a wireless duplex communication system, and also to a method of operating such a system. The invention is particularly applicable to Wireless Local Loop (WLL) Time Division Duplex (TDD) digital systems, and is therefore described below with respect to such systems.
Wireless radio communication is subject to the adverse effects of signal fading and multi-path reflections in which the received signal exhibits distortion and fluctuations in strength. This in turn detrimentally affects the reliability of the communication link. Space diversity is a well known technique for coping with such phenomena. Generally, the term xe2x80x9cspace diversityxe2x80x9d refers to the technique wherein the system uses two or more receiver antennas and selects the better antenna. The two antennas head in the same direction but are physically spaced from each other so as to have little correlation with respect to interferential fading or multi-path reflections, and do not undergo deterioration in quality at the same time.
Space diversity may be applied to both the uplink and downlink transmissions using the two antennas spaced apart in a way that minimizes the correlation between the signals at the antennas. Hence, a base station system is normally comprised of three units: the base station hardware circuitry box, and the two antennas. S/N evaluation for each antenna is accomplished either by switching the antennas to a single receiver (a time-consuming in-line process), or by applying a receiver to each antenna for simultaneous reception (hardware consuming). The signal from the better receiving antenna is further processed and is used for controlling the downlink transmission.
WLL systems operating in high density populated urban areas have to deal with high traffic capacity situations, which leads to solutions of multiple, co-located base stations. Because of the large number of units, and the required spacing between the antennas, multiple co-located base station systems, each utilizing space diversity, demand a substantial amount of installation space, i.e., tower height and/or volume, popularly known as xe2x80x9cChristmas Treexe2x80x9d sites.
Environmental regulations, customer requirements for a less conspicuous distribution site and for a more aesthetic appearance, simplified installation processes, and significant reduction of the currently-high installation costs and resources, all demand a more efficient system configuration than the existing ones.
An object of the present invention is to provide a wireless duplex communication system, and also a method of operating a communication system, having advantages in the above respects.
Another object of the present invention is to provide an improved diversity transmission and reception architecture and method particularly useful for WLL TDD co-located multiple based stations, which architecture and method reduce significantly the number of antennas in each site and minimize the installation process and resource requirements.
According to one aspect of the present invention, there is provided a wireless duplex communication system, particularly for high density service areas serviced by a plurality of radio port units each including receiver-transmitter circuitry and an antenna; characterized in that each radio port unit further includes: a first port for connecting the receiver-transmitter circuitry of the radio port unit to the antenna of another radio port unit in the same service area; and a second port for connecting the antenna of the radio port unit to the receiver-transmitter circuitry of the other radio port unit; whereby each of the two radio port units shares the antenna of the other radio port unit to provide space diversity.
According to further features in the preferred embodiments of the invention described below, the receiver-transmitter circuitry of each radio port unit includes: a first receiver; a second receiver; a transmitter; a multi-port coupler for splitting the signal energy received by the antenna of the radio port unit and for directing a portion thereof as a first signal to the first receiver of the respective radio port unit, and another portion thereof as a second signal to the second receiver of the another radio port unit, such that the first receiver of each radio port unit receive signals from the antenna of the respective radio port unit, and the second receiver of each radio port unit receives signals from the antenna of the another radio port unit; and a selector for selecting the antenna providing the better received signal for connection to the transmitter of the respective radio port unit for transmission.
According to further features in the described preferred embodiments, each radio port unit includes: compensation circuitry in the receiver path to the multi-port coupler to compensate for losses in the multi-port coupler; compensation circuitry in the transmitter path to compensate for losses in the multi-port coupler; and isolation circuitry between the transmitter of the respective radio port unit, and the transmitter in the another radio port unit to be connected thereto, to reduce intermodulation products in the transmitted signal.
According to still further features in the described preferred embodiments, the radio port units are enclosed within boxes, each box including within it at least one radio port unit, its antenna, and its receiver-transmitter circuitry, each box further including first and second ports exposed externally of the box for connection to corresponding ports in a radio port unit of another box.
As will be described more particularly below, the invention may be implemented in a communication system wherein some of the boxes in the services area are: of the single radio port configuration wherein the box includes a single antenna, a single radio port unit, and a two-port coupler for coupling its antenna to another box; and/or of a dual radio port configuration wherein each box includes a single antenna, a single radio port unit, and a two-port coupler for coupling the respective internal antenna to another box; and/or of a dual radio port coupler configuration wherein each box includes a single antenna, two radio port units, and a four-port coupler for coupling the respective internal antenna to each of the two radio port units of its box as well as to each of the two radio port units of another box.
An advantage of this invention is that the Radio Port Coupler (RPC) maintains the flexibility to perform as a conventional base station system in cases where special antennas are required (i.e., omnidirectional, hi-gain, 120xc2x0 sector. etc.), for applications of single base station sites, or different sector angle configurations. Reconfiguration of the RPC is simple and can be performed in the field as it merely involves unplugging the internal antenna and relocating an internal coaxial cable. Also, built into the RPC is the flexibility to perform as a conventional base station system using the internal antenna and a single external antenna for space diversity.
According to another aspect of the present invention, there is provided a method of operating a wireless duplex communication system in a high density service area, comprising: providing the service area with a plurality of co-located radio port units located spatially apart from each other; providing at least some of the radio port units with a single antenna; and externally connecting each of the radio port units having a single antenna to the antenna of another radio port unit heading in the same direction to enable each radio port unit provided with a single antenna to share the antenna of another radio port unit in order to produce space diversity for improving single reception under fading and multi-path channel conditions.
As will be described more particularly below, the present invention improves the facilities of a co-located cluster of fixed base stations which communicate with fixed subscriber units, and provides a space diversity system which reduces error probability caused by fading and multi-path channel conditions. Installations may thus be erected with a large number of co-located base stations in a substantially reduced installation space, while still complying with environmental regulatory requirements and also producing a more pleasing aesthetic appearance.
Further features and advantage of the invention will be apparent from the description below.